Write two observations when copper nitrate is heated.

Identify the salt Q from the following observation:

Salt Q is white in colour. On strong heating, it produces buff-yellow residue and liberates a reddish-brown gas. Solution of salt Q produces chalky white insoluble precipitate with an excess of ammonium hydroxide.

Identify the salt P from the following observations:

Salt P has light bluish-green colour. On heating, it produces a black coloured residue. Salt P produces brisk effervescence with dilute $\mathrm{HCl}$ and the gas evolved turns lime water milky, but no action with acidified potassium dichromate solution.

State one relevant observation for the following reactions:

• Zinc carbonate is heated strongly.

Identify the type of reaction:

$2{\mathrm{PbO}}_2\to 2\mathrm{PbO}+{\mathrm{O}}_2$